Hi paisley,
I don’t think your question can be answered in the quite the way you asked it because there are many factors that are involved in the durability of a mattress that you can read about in post #4 here. In other words durability is relative to many things including the person on the mattress and the same material that could be used in a durable mattress in one design may not be as durable in another design where the layer was in a different place in the mattress or had other materials above or below it or was in a two sided mattress.
Polyfoam, latex, memory foam, microcoils, and natural fibers can all last longer than 5-6 years in combination with an innerspring in a well designed mattress.
A brand is just a label on a mattress and it’s always much more effective to evaluate a mattress based on the specific design and materials that are inside it than it is to go by brands. Designs change on a regular basis and I don’t keep records of specific mattresses based on their construction or materials (which would be an impossible job). The better brands and the ones I would focus on are the ones that disclose what is in their mattress so you can make meaningful assessments and comparisons with other mattresses. As a general rule I would tend to avoid memory foam that was less than 4 lbs and polyfoam that was less than 1.8 lbs (1.5 lbs with some caution in some constructions) in amounts more than around an inch or so. When there is more than 2" of lower quality foam in the upper layers of a mattress it can become the weak link of the mattress.
Their latex mattresses use good quality materials but like any mattress their other mattresses are only as good as the construction and quality of the materials inside which is the only way to evaluate any mattress. They are also not in the best value range. They have also lost a lot of their retailers since they went bankrupt and were bought by Spring Air Sommex. They certainly wouldn’t be my first choice.
When they are made the right way (which the super premium brands do) then yes. Natural fibers will become firmer as they compress over time but they are very durable. Lumpy mattresses are usually from materials that have compressed into the coils and are usually a sign of poor construction.
Comfort layer materials are listed in this section and support layer materials are listed in this section. The choice between materials is a preference and all materials have good and worse quality versions. The only common material that doesn’t have its own section is gel memory foam because the information is still evolving as new materials reach the market but post #8 here and the links it includes has more information about these.
Phoenix